Anatectic record and contrasting <i>P–T</i> paths of aluminous gneisses from the central Grenville Province
Bibliographic record
Abstract
Abstract Anatectic aluminous gneisses, some derived from sedimentary rocks of broadly pelitic composition and others from hydrothermally altered felsic volcanic rocks, are exposed in the mid‐ P and high‐ P segments of the hinterland in the central Grenville Province. These gneisses consist dominantly of garnet, biotite, K‐feldspar, plagioclase and quartz, with sillimanite or kyanite, and display microstructural evidence of anatexis by fluid‐absent reactions consuming muscovite and/or biotite. Melt‐related microstructures, such as inter‐granular films and/or interstitial quartz or feldspar enclosing relict phases, are most abundant in the metasedimentary samples. Despite anatexis at granulite facies conditions, the hydrothermally altered rocks preserve earlier features attributed to the circulation of hydrothermal fluids, such as sillimanite seams, dismembered quartz veins and garnet‐rich aluminous nodules in a K‐feldspar‐dominated matrix. Microstructural and mineral chemical data, integrated with P–T pseudosections calculated with thermocalc for the metasedimentary rocks, permit qualitative constraints on the P–T paths. Data from a high‐ P kyanite‐bearing sample are consistent with a steep prograde P–T path up to ~14.5 kbar and 860 – 900 °C, followed by decompression with minor cooling to the solidus at ~11 kbar and 870 °C. This pressure‐dominated P–T path is similar to those inferred in other parts of the high‐ P segment in the central Grenville Province. In contrast, the P–T path predicted from a mid‐ P sillimanite‐bearing paragneiss has a strong temperature gradient with P–T of ~9.5 kbar and 850 °C at the thermal peak, and a retrograde portion down to ~8 kbar and 820 °C. In a broad sense, these two contrasting P–T patterns are consistent with predictions of thermo‐mechanical modelling of large hot orogens in which P–T paths with strong pressure gradients exhume deeper rocks in the orogenic flanks, whereas P–T paths with strong temperature gradients in the orogenic core reflect protracted lateral transport of ductile crust beneath a plateau.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".